1. Field of the Invention
The invention is directed to an efficient power management method and apparatus for providing multiple supply voltages from a single voltage source.
2. Description of the Related Art
In modern fourth generation wireless handset solutions, there is an expectation that a power management integrated circuit (PMIC) will generate an array of voltages of different values for powering various blocks, including for example digital cores, inputs/outputs, analogue circuits and power amplification stages. These blocks will have different voltage requirements. The voltages will be required to be generated from a single lithium ion cell having a terminal voltage with a typical value between 2.6V and 5.5V.
In order to provide this a so-called H-bridge buck-boost topology, as illustrated in FIG. 1, is typically provided.
With reference to FIG. 1, there is shown a voltage generation stage 100. A voltage source 110, typically a battery, provides an input voltage on line 112. Switching control elements consist of a buck section 104 formed by switches 102 and 103, and a boost section 109 formed by switches 105 and 106. Capacitor 107 is a capacitive storage element and inductor 108 is an inductive storage element. The voltage source 110 has an exemplary voltage supply of 2.5V. Supply stage 100 has to switch between buck and boost modes to control an output voltage on line 114.
In boost mode, the voltage source 110, typically a battery, has a value which is lower than a desired voltage at the output 114. In buck mode the voltage source 110 has a value which is higher than a desired voltage at the output 114.
A problem with the topology such as illustrated in FIG. 1 is that a separate voltage generation stage 100 must be used for each voltage required to be generated. That is, a voltage generation stage is dedicated to generating one voltage and, and when n voltages are required n voltage generation stages 100 are required. Thus the entire circuit of FIG. 1 must be replicated for each required voltage. This results in a number of buck-boost circuits, and in particular an associated proliferation of inductors. This adds to cost, takes up space, and generates interference.
In order to overcome these problems, in the prior art there has been proposed approaches to improve power management ICs. These approaches include: the provision of on-chip inductors; switched capacitor solutions; and multi-winding transformers.
It has been more recently proposed, in UK patent application number 0808873.4 (Nujira Limited) filed 15 May 2008, to provide a voltage generation apparatus comprising: a voltage source; an inductor, wherein a first terminal of the inductor is switchably connected to the voltage source; and a plurality of capacitors switchably connected to a second terminal of the inductor, wherein a respective plurality of voltages are formed across the plurality of capacitors. Thus using a single inductor, a single set of buck switches, a single set of boost switches, and n capacitors, n supply voltages can be generated.
It is an aim of the invention to provide an improved power management arrangement for the provision of multiple voltage levels for such an arrangement.